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Strongly weathered phyllite is a metamorphic soft rock widely distributed in the central and western regions of China. Due to its inadequate engineering properties, the direct use of this material as a roadbed filler is not feasible and requires improvement. In this paper, calcium acetate Ca(CH 3 COO) 2 , magnesium acetate Mg(CH 3 COO) 2 and calcium chloride CaCl 2 are prepared to improve the filler by microbially induced carbonate precipitation (MICP). The effects of different calcium and magnesium sources on porosity, water absorption, uniaxial compressive strength, crack propagation time and failure patterns are investigated. The results show that CaCl 2 and Ca(CH 3 COO) 2 exhibit the most significant enhancement effect in reducing porosity and water absorption, increasing the uniaxial compressive strength by over 30%, delaying the time of failure occurrence and reducing the number of tensile cracks significantly. X-ray diffraction (XRD), scanning electron microscopy (SEM) and pore size distribution analyses reveal disparities among the rock samples. CaCl 2 and Ca(CH 3 COO) 2 have greater efficacy than Mg(CH 3 COO) 2 in terms of improvement, as they generate relatively many carbonate precipitates to bind the phyllite filler and reduce the size and quantity of pores. To avoid the corrosion of Cl- ions when adding reinforcement bars in actual engineering, Ca(CH 3 COO) 2 is an ideal calcium source for improving the strongly weathered phyllite filler. • The physical and mechanical properties of strongly weathered phyllite filler can be improved after modification. • The physical properties and strength of modified sample have a relationship with carbonate content and crystal morphology. • Calcium acetate is suggested for use as the calcium source to improve the strongly weathered phyllite filler. [ABSTRACT FROM AUTHOR]

Highlights • Study on steel fibers reinforced steel reinforcement concrete composite beams under four point bending. • Adding steel fiber can slightly improve flexural capacity. • The higher the volume of steel fiber, the slower and more stable the descending segment of curve would be. • Steel fibers can be an alternative to shear reinforcement for SRC beams. • Formulas for predicting the bearing capacity of SFSRC beams are proposed. Abstract In this paper, an innovative method to replace steel reinforcement cage by steel fiber to form a steel shape and steel fiber reinforced concrete has been proposed to solve the problems of steel reinforced concrete structure during construction, such as position conflict between shape steel and steel bars, or difficulty of concrete placement, etc. Eighteen beams were tested under a four-point bending configuration to study the effectiveness of steel fibers on shear and flexural strengths, failure mechanisms, crack control, and ductility. The major factors considered were shear span depth ratio (λ = 2.5, 3.5), with or without longitudinal reinforcement and web reinforcement (none, stirrups and/or steel fibers). The response of Steel Fiber Steel Reinforcement Concrete (SFSRC) beams were assessed depending on the results of crack patterns, load at yielding, failure and ultimate bearing capacity, failure modes, ductility and displacement increment of plastic development, The experimental results showed that the addition of steel fibers improves the mechanical response, specifically speaking, flexural and shear strengths and ductility of the tested specimens. The longitudinal reinforcement can greatly enhance the bearing capacity, and the stirrups and steel fibers can make the reinforcement effect more prominent. The stitching effect of steel fiber between cracks leads to stable bearing capacity of the specimens always stable after the peak load. Increasing the content of steel fiber contributes to delay or even avoid bond failure. Steel fibers can be an alternative to shear reinforcement. A formula was proposed to predict the bearing capacity of SFSRC specimens, and the comparison between predictions and experiment results proved the reasonable of the formula. A formula was proposed to predict the bearing capacity of SFSRC specimens, and the comparison between predictions and experiment results proved the the formula. [ABSTRACT FROM AUTHOR]

Highlights • Bond of GFRP bars in high strength concrete was investigated using hinged beams. • Bond performance was studied with showing the effect of main parameters on bond. • Design code predictions were compared to the experimental results. Abstract Although several research studies have been conducted on investigating the bond stress – slip behaviour of Glass-Fibre Reinforced Polymer (GFRP) bars embedded in high strength concrete (HSC) using a pull-out method, there is no published work on the bond behaviour of GFRP bars embedded in high strength concrete using a hinged beam. This paper presents the experimental work consisted of testing 28 hinged beams prepared according to RILEM specifications. The investigation of bond performance of GFRP bars in HSC was carried out by analysing the effect of the following parameters: bar diameter (9.5, 12.7 and 15.9 mm), embedment length (5 and 10 times bar diameter), surface configuration (helical wrapping with slight sand coating (HW-SC) and sand coating (SC)) and bar location (top and bottom). Four hinged beams reinforced with 16 mm steel bar were also tested for comparison purposes. The majority of beam specimens failed by pull-out. Visual inspection of the test specimens showed that the bond failure of GFRP (HW-SC) bars usually occurred owing to the bar surface damage, while the bond failure of GFRP (SC) bars was caused due to the detachment of sand coating. The GFRP bars with helical wrapping and sand coated surface configurations showed different bond behaviour and it was found that the bond performance of the sand coated surface was better than that of the helically wrapped surface. Bond strength reduced as the embedment length and bar diameter increased. It was also observed that the bond strength for the bottom bars was higher than that of the top bars. The bond strength was compared against the prediction methods given in ACI-440.1R, CSA-S806 and CSA-S6 codes. All design guidelines underestimated the bond strength of both GFRP re-bars embedded in high strength concrete. [ABSTRACT FROM AUTHOR]

Highlights • Present applications of SHPB in characterization of various cement-based materials. • Details of experimental tests on different concrete and UHPC under high rate of loading. • Data and information about specimen and fiber geometries on experimental studies. • Summarized results of numerical simulations on cement-based materials under test by SHPB. Abstract Our living standards are substantially influenced by the advent and development of new materials. The need for stronger building materials has led to useful innovations such as the fortification of concrete to produce Ultra-High-Performance Concrete (UHPC). Since numerous structures constructed by various types of concrete and UHPC, experience high rate of loading in their service life, reliable databehavior of this material is an important issue. In the current study, the behavior of different reinforced and unreinforced concrete, and also various UHPCs with and without fiber are comprehensively reviewed based on experiments by Split Hopkinson Pressure Bar (SHPB). The investigated parameters for the tests performed included matrix constituents, temperature condition, sample size, fiber material, and loading rate. The available results indicate that Ultra-High-Performance Fiber Reinforced Concrete (UHPFRC) is the most favorable material for utilization in impact-resistance structures. Since the fibers show crucial role in the dynamic strength, fibers material and their aspect ratio should be selected precisely. Applications of numerical simulations can significantly accelerate the material development process, therefore results of computational constitutive modeling are also presented in this paper. The summarized data can be used not only for comparison and the improvement of load carrying capacities of cement-based materials, but also can be beneficial in the development of new computational models. [ABSTRACT FROM AUTHOR]

Abstract: It is common practice these days to retrofit reinforced concrete (RC) beams and slabs by adhesive bonding FRP or steel plates to their surfaces. However, research has shown that these external plates can debond prematurely at relatively low strains such that the ability of the plated section to redistribute moment to other sections is severely limited and to such an extent that guidelines often preclude moment redistribution. This restriction may severely limit the use of plating in buildings where ductility is a requirement. Tests on steel and FRP plated continuous beams have shown that moment redistribution can occur and a design procedure has been developed to determine the amount of moment redistribution for any type of adhesively bonded plated section, and for any type of plate material, such as steel or FRP plates. In this paper, an analysis approach to quantify the amount of moment redistribution is described and the concepts of positive and negative moment redistribution introduced. A parametric study is then used to illustrate how the plate material and geometric properties affect moment redistribution; in particular, the study looks at the effect of using carbon FRP plates and glass FRP plates, as well as steel plates that have been designed to either debond prior to yielding or yield prior to IC debonding. In summary, the paper will show that plated sections can redistribute moment and, hence, the present restriction can be removed which should extend the use of retrofitting by plating. Furthermore, the moment redistribution analysis procedure allows the engineer the freedom to choose the properties of the plate to design for moment redistribution. [Copyright &y& Elsevier]

Highlights • This study examines the cyclic behavior of superelastic SMA bars with BRDs under tension–compression cycles. • The material properties of typical interest in seismic applications are evaluated. • The reversed compression loading benefitted SMA behavior in the cyclic tension–compression tests. Abstract Shape memory alloys (SMAs) show great potential in seismic applications because of their appealing superelastic feature and good energy dissipation capacity. The tensile behavior of SMA wires and bars has been extensively studied over the past decades. However, little attention has been paid to their compressive properties under cyclic loading. Thus, this paper presents a systematic experimental study on the cyclic behavior of superelastic SMA bars with buckling-restrained devices (BRDs) when subjected to tension–compression cycles. The detailed design of BRD is described first. The material properties such as “yield-like” strength, peak strength, self-centering capability, and energy dissipation of typical interest in seismic applications are evaluated with varying strain amplitudes, strain rates, and loading protocols. Test results show that satisfactory and stable flag-shaped hysteretic loops without any strength degradation are obtained in multiple loading cycles under cyclic tension–compression loading. Moreover, the SMA bars exhibit remarkable self-centering capability that is nearly independent of strain rate and loading protocol. [ABSTRACT FROM AUTHOR]

This paper reports the loss of concrete stiffness due to the adverse effect of alkali-silica reactivity (ASR). The concrete cylinders prepared with fourteen aggregate groups were immersed in water at 20 °C (68°F), and in the 1.0 N NaOH at 80 °C (176°F). The percent loss in stiffness (PLIS) between water- and alkali-cured cylinders was determined at 4 and 26 weeks, and was correlated with the expansion of the mortar bars (immersed in the 1.0 N NaOH at 80 °C (176°F)) containing the companion aggregate source at the test durations of 2, 4 and 8 weeks. The results concluded that the loss in stiffness of the concrete cylinders occurred at 4 weeks, and it significantly increased at 26 weeks. The study also suggested that the ASR classification of the aggregates based on the expansion limits of mortar bars showed a good correlation with that produced from the proposed limit of stiffness loss of concrete. [ABSTRACT FROM AUTHOR]

There is distinctive difference in the coefficient of thermal expansion (CTE) between fiber reinforced polymer (FRP) bar and surrounding mass, which may generate great transverse thermal pressure at their interface and cause significant reduction in bond strength of FRP tendon. However, the transverse thermal pressure predicted from previous analytical model has marked deviation from that obtained from experiment test. This paper presents an improved analytical model to exactly analyzing the transverse thermal pressure at the interface of FRP bar/surrounding mass and the three-dimensional thermal stresses of FRP bar. Then accurate measurement using fiber Bragg grating (FBG) sensor is conducted to obtain the transverse thermal pressure that agrees well with our theoretical result. Our work may be helpful in improving the thermal compatibility and bond performance of FRP tendon. [ABSTRACT FROM AUTHOR]

In this paper, the propagation of chloride-induced corrosion of bars embedded in reinforced concrete (RC) beams exposed to a chloride environment was examined. These bars were exposed to chloride environment for various periods. Then, the cracking of the RC beams was observed and the corroded reinforcements were extracted from the beams in order to investigate the corrosion distribution and propagation. The cross-sectional loss and spatial distribution in the longitudinal direction were studied by cutting the residual reinforcement into several small specimens. By analysing the cross-sectional loss results, it was found that the corrosion developed in a stochastic way. However, the corrosion zone developed gradually from the mid-span of the beam to the two ends, and there was a linear relationship between the extent of the corrosion zone and the corrosion period. Similarly, the degree of pitting corrosion and general corrosion also increased. The relationship between pitting corrosion and general corrosion developed along an improved exponential curve, while the pitting factor and the general corrosion showed a logarithmic relationship. The results of this investigation could be treated as an envelope curve, which can be helpful to assess the corrosion state of reinforcements situated in aggressive environment and predict the residual life-cycle of corroded constructions. [ABSTRACT FROM AUTHOR]

Effective post-yield stiffness of reinforced concrete (RC) columns can significantly contribute to the seismic performance of RC structures. However, because of the elastoplastic properties of steel bars, the post-yield stiffness of an ordinary RC column can be very slight or even negative. Fiber reinforced polymer (FRP) can provide a high degree of ultimate strength, light weight, and protection from corrosion. By combining steel and FRP, a designable post-yield stiffness can be achieved for concrete structures reinforced with steel-FRP composite bars (SFCBs) or hybrid steel/FRP bars. This paper conducted cyclic loading tests on four concrete columns with different reinforcement types, including steel bars, hybrid steel/FRP bars, and SFCBs. The test results showed that (1) the columns reinforced with different bars had similar strain distributions from column base to cap prior to yielding. After yielding, the plastic deformation of the ordinary RC column concentrated at the column base and the loading capacity decreased with the increase of lateral drift because of the P - δ effect. (2) Unlike the negative post-yield stiffness of an ordinary RC column, the post-yield stiffness of a column with hybrid reinforcements was positive. As the post-yield stiffness ratio of the longitudinal reinforcement increased by 27 percent, the post-yield stiffness of the concrete column increased by 7.4 percent. Therefore, the corresponding displacement ductility could reach 11—much greater than that of the RC column (6.28). (3) As a result of the more robust hysteretic curve of the RC column, the equivalent viscous damping coefficients of the RC column were greater than those of the hybrid column, whereas the hybrid reinforced concrete columns could dissipate earthquake energy without a corresponding loss of strength. [ABSTRACT FROM AUTHOR]

This paper investigates the bond-slip behaviour of steel reinforcement embedded in engineered cementitious composites (ECC), a ductile concrete exhibiting tensile strain hardening performance. Two series of experimental tests were carried out on short and long reinforcement subject to pull-out actions. The maximum bond stress that embedded steel reinforcement could sustain was quantified through pull-out tests on short rebars. Experimental results of short reinforcement suggested that ECC significantly increased the maximum bond stress of steel reinforcement. For long reinforcement, special attention was paid to the bond stress of steel segments at post-yield stage. Bond stress profiles were determined in accordance with attached strain gauge measurements along the steel bars. Besides, the effect of localised necking beyond ultimate strength on the force-slip relationships of reinforcement was studied. Thereafter, an analytical model was proposed based on experimental results to predict the force-slip relationship of long reinforcement either anchored in concrete or in ECC. Reasonably good agreement was achieved between experimental and analytical force-slip curves. Finally, parametric studies were conducted to quantify the required embedment length of steel reinforcement in ECC. [ABSTRACT FROM AUTHOR]

The bond strength of plain round bars, which is important for the assessment of historical buildings, is greatly influenced by the lateral stress state. To predict the bond strength of plain round bars subjected to lateral tension, a few empirical models were presented based on test results. However, these models are probably restricted for application since the test parameters adopted in the experiment are limited. Therefore, an analytical study, which is independent of test parameters, is made in this paper to investigate the bond behavior of plain round bars embedded in concrete subjected to uniform lateral tension. Based on the theory of elasticity, an analytical solution for the ultimate bond strength is derived. When the shrinkage of concrete and the geometric and mechanical parameters of bars and concrete are provided, the analytical solution can be used to evaluate the ultimate bond strength of plain round bars subjected to uniform lateral tension. 72 pull-out specimens are made and tested to verify the analytical solution. The results show that, the analytical predictions are in good agreement with the experimental results. Finally, a sensitivity analysis is made to evaluate the effects of main factors on the ultimate bond strength of plain round bars, and a simplified model is provided for practical applications. [ABSTRACT FROM AUTHOR]

Bond durability tests on steel-fiber reinforced polymer (FRP) composite bars (SFCBs) with sea sand concrete and river sand concrete in simulated ocean environments are conducted in this paper, and steel bars are also used for comparison. Two types of environments, seawater immersion and seawater wet–dry cycling, are adopted. Sixty-six pullout specimens are prepared, and the variations of bond performance after 30, 60 and 90 days of aging are tested and comparatively analyzed. The test results showed that, with respect to the bond–slip curves, wave-shaped descending branches were observed for SFCBs; the bond strength between SFCBs and sea sand concrete in a wet–dry cycling environment at all ages were improved. However, with regard to the steel bars in the same condition, the surfaces were rusted, and the bond strengths showed a decreasing trend. Immersion in 40 °C seawater reduced the bond performance of SFCBs with concrete, whereas the rust process of steel bars slowed down due to the lack of fresh oxygen. [ABSTRACT FROM AUTHOR]

Present paper investigates the efficiency of basalt fiber reinforced polymer bars (BFRP) for near surface mounted (NSM) strengthening of RC beams. An experimental program was carried out to determine the pullout behavior of BFRP bars and based on the results, an BFRP-NSM method has been designed. To assess the bond behavior of BFRP to concrete, pullout tests were carried out. The influences of bonded length, groove size and diameter of bar on the bond behavior were analyzed. Based on the results, a ratio of groove size to diameter has been proposed to utilize the maximum potential of BFRP bars in NSM strengthening. Flexural strengthening of RC beams were carried out by using BFRP-NSM method. The diameter of the bar, number of bar and groove size were considered as the influencing parameter. Based on the studies, it is concluded that it is possible to double the load carrying capability without loosing ductility by using this method. [ABSTRACT FROM AUTHOR]

The use of near-surface mounted (NSM) FRP composites for strengthening RC beams in flexure has become increasingly popular in the last decade. Compared to the externally bonded (EB) FRP strengthening method, the bond between FRP and concrete is much stronger when the NSM FRP strengthening method is used. However, debonding is still a likely failure mode in RC members strengthened with NSM FRP bars. The debonding in an NSM FRP-strengthened beam may initiate from either of the two ends of an NSM bar (i.e. end debonding) in the form of interfacial debonding or concrete cover separation, both of which are closely related to the existence of large localized interaction forces between the NSM bar and concrete near the bar ends in such beams. This paper presents an analytical solution for the interaction forces in RC beams strengthened with NSM FRP round bars, which are one of the most popular types of FRP bars used for NSM strengthening. The key elements of the proposed analytical solution are two interfacial stiffness parameters (i.e. tangential interfacial stiffness and normal interfacial stiffness). The validity of the proposed analytical solution is also verified using a sophisticated 3D FE model of a RC beam strengthened with a NSM round bar. [ABSTRACT FROM AUTHOR]

In wood-based structural design, in addition to the criteria of strengthening and stiffness, the criterion of deformability due to the creep of wood, especially in horizontal members, is a factor that often limits the design. New developments have further improved the structural performance, such as the strengthening of timber (glulam) beams by bonding composite material combined with an ultra-high performance fiber reinforced concrete (UHPFRC) that is internally reinforced with or without carbon fiber reinforced polymer (CFRP) bars. Glulam, UHPFRC and CFRP may be an interesting composite mix for responding to the problem of the creep behavior of composite structures made of different materials with different rheological properties. This paper describes an experimental and analytical investigation on the short-term and long-term (creep) performances of glulam–UHPFRC–CFRP beams. The experimental investigations of creep behavior were conducted in indoor and outdoor environments under constant loading for approximately 1 year. The measured results are compared to the results from an analytical model. This model was developed to predict the creep response of the glulam–UHPFRC–CFRP beams based on the creep characteristics of the individual components. The results indicate that heterogeneous glulam–UHPFRC beams improve both strength and stiffness and can also effectively reduce the creep deflection of wooden beams. [ABSTRACT FROM AUTHOR]

This paper presents a practice-oriented method for design of flexural concrete members for a given service life in an aggressive environment. A time-dependent correlation between rebar corrosion level in terms of mass loss and its bond strength degradation at the steel–concrete interface, and the ultimate flexural and shear resistances of the reinforced concrete elements is evaluated using basic electrochemistry and empirical relationships. The design development length is determined based on the mass loss prediction and the equation depicting loss of bond strength with mass loss due to corrosion. The results show that the mass loss of rebars depends on several factors, such as the surface chloride concentration, cover thickness to rebar and concrete permeability, rebar size and ratio of the concrete cover thickness to the rebar diameter ( c/d b ratio). The model results predict the required development length at the end of the service life of 70 years to be more than twice that obtained from conventional reinforced concrete design. The proposed durability design procedure is illustrated with the help of a detailed design example. Analysis results show that because of corrosion the flexural and shear strengths decrease by about 80% and 52%, respectively, after the service life of 70 years. [ABSTRACT FROM AUTHOR]

Abstract: The use of FRP bars and strips as near-surface mounted (NSM) reinforcement has become an emerging technique for the strengthening of reinforced concrete (RC) members. The bond between NSM FRP reinforcements and concrete is a crucial factor affecting the efficiency of this technique. Many factors involving the interaction between FRP reinforcement, adhesive and concrete can affect the bond behaviour and failure load of the NSM strengthening system. In this paper, the modified pullout test (adapted to NSM reinforcement) is used to study the effect of groove surface (pre-formed and saw cut), groove geometry (dimensions and shapes), FRP bar type (material and surface treatment), bond length; and also of the incorporation, in the groove–concrete system, of different construction details that modify the NSM–concrete interaction (transverse interlocking with or without shear connectors, covering plate with shear connectors and confinement of surrounding concrete). The tested specimens had different bond behaviours and modes of failure: bar–epoxy interface failure, epoxy failure with concrete splitting, concrete–epoxy interface failure and tensile failure of the concrete specimen. The effects of the introduced variables on the response of the specimens are presented and discussed. [Copyright &y& Elsevier]

Abstract: Area loss of corroded rebar cross sections is a crucial variable that is difficult to measure. In this paper, virtual models of corroded bars were built using 3D laser scanning technology; and, 693 severely corroded sections were screened to explore a practical way for the area loss determination. The results show that residual sections can be simplified into ellipses for general corrosion; otherwise, it can be ascribed to combined pit and general corrosion. Four spot penetration depths were taken as independent variables which can be easily measured. Based on the variables, regression models were developed and proven to be effective. [Copyright &y& Elsevier]

Abstract: The paper aims to investigate the influence of simultaneous loading and reinforcement corrosion on the structural performance of concrete beams. Five reinforced concrete beams were first loaded to 60% of their strengths, and then subjected to the sustained load and reinforcement corrosion simultaneously, until they collapsed either due to corrosion development or further loading. The experimental results indicate that, under the same loads, the time-dependant deflections of corroded beams increased more rapidly than those of non-corroded beam, and reached their limiting deflections prematurely. A local corrosion of a shorter length of tensile bars decreased beam strength and ductility more greatly than an extensive corrosion of a longer length of bars. Simultaneous loading and corrosion impairs beam strength and ductility more significantly than separate one. Either a further corrosion or an occasional over-loading or both are likely to cause concrete structures under service loads to collapse suddenly without significant deflection. [Copyright &y& Elsevier]

Abstract: In the present work, the behavior of inoxydable steel and their performance as reinforcement bars in concrete structure is being investigated. Focus is given on the interaction behavior with concrete and the tension stiffening phenomenon. This study highlighted an approach to observe this interaction behavior in bending test instead of direct tension as per reported in many references. The approach and strategies applied is easier to set up and is able to observe the tension stiffening behavior in composite concrete beam. Finally, the constitutive law developed and the tension stiffening properties are then applied to numerical finite element analysis (FEA) to verify their correlation with actual behavior. Comparison with laboratory results shows a good correlation between the two. To conclude, the constitutive law provided in this paper has very good resemblance to the actual behavior of austenitic and therefore useful to represent the inelastic properties of these steels in any numerical modeling work. Tension stiffening parameters used is acceptable and the modeling strategies made in Abaqus can closely represent the actual condition. [Copyright &y& Elsevier]

Abstract: Temperature and moisture content are the main factors that influence concrete carbonization, chloride diffusion, and corrosion rate of reinforced bars placed in concrete. Climate variations can induce the variation of the micro-environment of concrete. Therefore, temperature and relative humidity in the natural climate environment serve as the climate load, and the variations in the micro-environment corresponding to the climate variations are the effect of the climate load. Based on these, the present paper attempts to build climate temperature and relative humidity action spectrums as a climate load model. The climate action spectrums of temperature and relative humidity are built based on meteorological data of the temperature and the relative humidity variations. The effects of sunshine and rain are included in the construction of the action spectrum. Series of tests are conducted under artificially controlled climate environment (ACCE) and natural climate environment (NCE) conditions to support the construction of the spectrum. [Copyright &y& Elsevier]

Abstract: The corrosion of steel reinforcement embedded in concrete bridge deck has been the cause of major structural deterioration and of high costs in repair and maintenance. Glass fibre-reinforced polymers (GFRP) bars provide a promising alternative reinforcement, which exhibit high durability in combination of high strength and light weight. Due to the low value of elasticity and brittle behaviour of FRP materials, the service behaviour of GFRP reinforced concrete structure is critical in the majority research with FRP bars for reinforcing concrete on simply supported beams and slabs. However, it is recognised that laterally restrained slabs such as bridge deck slabs exhibit compressive membrane action (CMA) which has a beneficial influence on load-bearing capacities and service behaviours such as deflections. This paper presents the results of an experimental study of one-third scaled concrete bridge deck models with several varying structural variables, including supporting beam sizes, reinforcement percentages and reinforcing materials. After the comparison the results of experimental models, the influences from these structural parameters on ultimate strengths and compressive membrane action were evaluated. Furthermore, the improvement of an existing theoretical model for GFRP reinforced concrete bridge deck slabs provided accurate predictions of load-bearing capacities. Consequently, a parametric study has been conducted and the results are discussed. [Copyright &y& Elsevier]

Abstract: In recent years there has been wide use of non-linear dynamic analysis for the evaluation of existing structures in areas of high seismic risk. In the simulation of the cyclic behaviour of elements in reinforced concrete (RC) its bonding performance cannot be ignored. There are numerous numerical models developed in recent decades which can explicitly account for the slip between reinforcing bars and the surrounding concrete through the definition of the local hysteretic bond–slip relationship. As for plain bars, commonly used in reinforced concrete buildings before the 1970s, there are almost no references to hysteretic bond mechanisms. This paper describes the results of a series of monotonic and cyclic pull-out tests aimed at the assessment of the bond performances of plain round bars. Monotonic behaviour is characterized by a first ascending branch, up to the maximum bond strength; in this phase, as the slip increases, chemical–physical adhesion and micro-interlocking between the cement paste and the indentations of the bar surface progressively activate. During post-peak phase the only frictional contribute is present, gradually degrading towards a minimum value as the slip increases. The two parameters, maximum bond strength and minimum frictional bond, in spite of the high variability shown, seem to reflect well the literature indications about bond performances of plain bars. In cyclic field, where the only frictional mechanism is present, experimental results show a significant degradation of bond capacities. Hysteretic cycles show a singular shape, characterized by a reloading phase showing a slight reduction for slip values approaching zero and a subsequent increase in bond stress towards the maximum imposed slip. Bond stresses in cyclic field show a high variability, but it is generally possible to recognize a decreasing trend both with the number of cycles and with the maximum imposed slip. [Copyright &y& Elsevier]

Abstract: Fiber-reinforced polymer (FRP) bars can be used as internal reinforcement for new reinforced concrete (RC) structures and as near-surface mounted (NSM) reinforcement for the strengthening of RC structures. The NSM method is an emerging strengthening technique for RC structures, where FRP bars are embedded into grooves cut in the cover of RC members. In both cases, strain monitoring of the FRP bars is desirable either for the investigation of the structural behavior or for the long-term health monitoring of the structure. This paper presents a study in which fiber-optic sensors were embedded into glass FRP (GFRP) bars to produce smart GFRP bars for NSM applications. The manufacturing process of the smart FRP bars is illustrated and their performance in tensile, bond and beam flexural tests is examined to assess the effectiveness of these smart FRP bars for achieving the dual purpose of structural strengthening and strain monitoring. On the basis of the test results, the advantages and limitations of fiber-optic sensors compared to electrical strain gages in the strain monitoring of NSM FRP bars are discussed. The bond and beam test results also confirm the effectiveness of the NSM method for the strengthening of RC structures. [Copyright &y& Elsevier]

Abstract: Performances of two different types of fiber reinforced concrete (FRC) beams, which are strengthened with three different types of fiber reinforced plastic (FRP) sheets, respectively, are analyzed in this paper. A series of four-point bending tests for beams are carried out to investigate the effect of fiber reinforcement on FRP sheet strengthening. Three types of concrete beams have been tested, which are plain concrete beams for reference, polypropylene fiber (PF) reinforced concrete beams, and polypropylene fiber (PF) together with steel fiber (SF) hybrid reinforced concrete beams. Three strengthening schemes have been used, which are mono-layered carbon fiber reinforced plastic (CFRP) sheet strengthening, mono-layered glass fiber reinforced plastic (GFRP) sheet strengthening and CFRP mixed GFRP bi-layer sheets strengthening, respectively. Crack developing mechanism and variations of displacements with curvatures for different beams are analyzed. Test and numerical simulation results show that PFs and SFs are able to control the propagation of micro cracks, the development of macro cracks in concrete, and to improve the concrete strength. The ultimate failure modes of test beams also chang from peeling-induced debonding into FRP rupture, which shows that the FRP sheets can exert its strengthening effect sufficiently. Test and numerical results indicate it is an effective method for CFRP mixed GFRP to strengthen FRC beams, which can improve the toughness of concrete, reduce strengthening cost and meanwhile enhance bearing capacity of concrete beams. [Copyright &y& Elsevier]

Abstract: The corrosion of steel poses a serious problem to the durability of reinforced concrete structures and fibre reinforced polymer (FRP) has emerged as a potential alternative material to the traditional steel. The results of a test series consisting of carbon FRP (CFRP) and steel bars reinforced concrete beams are reported in this paper. The results indicated that the behaviour of CFRP and steel reinforced beams was similar in many aspects. Both type of beams failed in their predicted modes of failure. The strength design method underestimated nominal moment capacity of CFRP reinforced beams. The deflection of CFRP reinforced beams was satisfactory at service load level, corresponding to theoretical load capacity. The deformability factor of CFRP reinforced beams was more than 6 indicating their ductile nature of failure. [Copyright &y& Elsevier]

Abstract: Carbon fibre reinforced polymer (FRP) laminates are increasingly being used to strengthen reinforced concrete beams. Monitoring the integrity of the adhesive bond between the laminate and the concrete is important to establishing the long-term reliability of this technique. This paper discusses the development of a strain-based index in which the loss of strain compatibility can be used to identify regions where debonding has occurred. Theoretical and experimental work was conducted and the laminate tensile strain profiles were shown to be sensitive to the presence of induced debonded zones. The method has potential for broad implementation in many field monitoring applications. [Copyright &y& Elsevier]

• The connection system of rein-filled steel pipe is proposed for FRP bars. • Tensile performance of rein-filled steel pipe splices of BFRP bars are investigated. • A method for calculating the ultimate tensile capacity of the splice is presented. The absence of effective connection methods for FRP (fiber reinforced polymer) bars is one of the limitations that restricts the widespread use of FRP bars in civil engineering. In view of this, a simplified connection method with the form of resin-filled steel pipe is proposed in the paper for FRP bars. Based on the tensile tests of 37 resin-filled steel pipe splices of BFRP (basalt fiber reinforced polymer) bars, the tensile performance of the proposed connection method was systematically investigated with the variables of epoxy resin type, epoxy resin layer thickness, BFRP bar diameter and BFRP bar anchorage length. The test results showed that, for splices with the same sectional configuration, the failure mode varies from BFRP bar pullout to BFRP bar rupture with the increase of the BFRP bar anchorage length. And for specimens fabricated with different BFRP bars in diameter, the critical anchorage length increased dramatically with the increase of the BFRP bar diameter. Besides, the tensile performance of the splices improved gradually with the increase of the epoxy resin layer thickness before 3 mm reached. In addition, the relative slip between the steel pipe and the BFRP bar is significantly affected by the elastic modulus of the grouted epoxy resin. The higher the elastic modulus is, the lower the relative slip is and vice versa. At last, an analytical method for calculating the ultimate tensile capacity of the resin-filled steel pipe splices of FRP bars is proposed based on a simplified bi-linear bond-slip model. The effectiveness of the method is verified with the comparison between the tested results and calculated ones. [ABSTRACT FROM AUTHOR]

• The applied additional ribs anchorage system was an efficient method to enhance the bond stuffiness and pull-out strength. • Additional rib anchorage system was obviously optimized and exhibited a very slight tensile strength loss of CFRP bars. • The existence of additional ribs transformed the bond stress transferring mechanism and thus delayed the occurrence of the concrete splitting. • Empirical expression in ultimate tensile stress that considers the influence of bond length was proposed. The slippage of fiber-reinforced polymer (FRP) bars in concrete occurs frequently because of the insufficient anchorage capacity of FRP bars in concrete, and it considerably affects the reliable application of FRP bars as reinforcing steel bars in civil engineering structures, especially in prestressed structures. In this paper, an optimized additional rib (AR) anchorage system was applied to the carbon-FRP (CFRP) bars to improve this weak anchorage characteristic of CFRP bars. The extrusion technology of the additional ribs was optimized, and only a slight deterioration of approximately 1.85% in the tensile strength of the CFRP bars was noted, compared to that corresponding to our previous extrusion technology (a loss of approximately 7.84%). Subsequently, pull-out tests were performed to investigate the influence of the number of additional ribs and bond length on the bond performance between the CFRP bars and concrete. The experimental results demonstrated that the existence of additional ribs, which produced an end pressure, transformed the bond stress transferring mechanism and reduced the radial force exerted on the surrounding concrete, thereby delaying the occurrence of the concrete splitting failure. In addition, the CFRP bars anchored with the additional ribs exhibited a remarkable enhancement in the pull-out strength, whereas this improvement was influenced by the embedment length of the CFRP bars and the ratio of the additional rib length to the bond length (l ar / L). Finally, an empirical expression to calculate the development length of the CFRP bars with and without an AR anchorage was proposed and compared with the expressions provided in the existing design standards. It was concluded that the applied AR anchorage system could effectively reduce the development length of the CFRP bars. Compared to that of the control specimens, there was approximately 16.7% decrease in the development length for the specimens anchored with one additional rib. [ABSTRACT FROM AUTHOR]